This invention relates generally to thermo electric coolers and temperature sensors and more particularly concerns a subassembly for a thermoelectric cooler and a temperature sensor which is easier to install, has fewer loose wires, better temperature maintenance and improved reliability.
Thermoelectric coolers are used in a wide variety of electronic applications where a component must remain either at a constantly maintained temperature or a specific temperature either warmer or cooler then the ambient temperature to work correctly. Thermoelectric coolers have a cold side and a hot side. A device to be either heated or cooled is put in contact with the cold side of the thermoelectric cooler while the hot side of the thermoelectric cooler is put in contact with a heat sink. If the device is to be cooled, the thermoelectric cooler removes heat from the device and adds heat to the heat sink. If the device is to be heated, the thermoelectric cooler removes heat from the heat sink and adds heat to the device. Thermoelectric coolers are often used with thermistors, which are used to sense temperatures and enable control of the thermoelectric cooler, commonly as an input to a thermoelectric cooler driver.
The thermoelectric cooler and the thermistor each have two wires that must be connected. The wires are fragile, difficult to handle, and susceptible to damage from handling because the wires can be as thin as 0.002 inches in diameter.
The thermistor is usually mounted on the cold side of the thermoelectric cooler or to a device being cooled. To properly regulate temperature, the thermistor must only sense the thermoelectric cooler cold side temperature or the device it is trying to cool, whichever it is mounted on. However, the electrical connection to the thermistor is through wires or pins at a substantially higher ambient temperature. As a result, the thermistor senses not only the cold side temperature of the thermoelectric cooler or device being cooled but also the higher ambient temperature through the thermal conduction of the wires or pins of the electrical connections. The thermistor as a result averages these two temperatures and sends a false feedback signal to the thermoelectric cooler driver. The overall result is an ambient dependent temperature control with a set point that varies according to changes in the ambient temperature. Tests of this phenomenon show this variation at between two degrees centigrade and seven degrees centigrade. In many cooling applications, variations of this magnitude are unacceptable.
In laser printing applications, thermoelectric coolers are used to cool laser diodes which have a strong temperature dependent optical power output. Variations as large as those cited cause unacceptable fluctuations in the ouput power of the laser diode. The unacceptable output power fluctuations in the laser diode cause additional expensive circuitry to be added to the system to maintain a constant optical power output from the laser diode.
Accordingly, it is the primary aim of the invention to provide a subassembly which reduces the sensing of the ambient temperature by the thermistor thereby providing a more accurate temperature control.
Further advantages of the invention will become apparent as the following description proceeds.